This invention relates generally to a carbonless copying system wherein the mating sheet surfaces are coated respectively with compatible initially colorless reactive components capable of reacting to produce a colored mark upon impact. More particularly, the invention relates to manifolded sets utilizing an initially colorless color forming system including an intermediate tissue ply or plies which are unprinted.
Manifolded sets of carbonless copying paper typically comprise three sheets with the top sheet thereof coated on its back surface with an encapsulated solution of a colorless color-former in a suitable solvent, the bottom sheet having its front surface coated (CF) with a solid material containing a record-developing material, and the intermediate sheet being coated front and back (CFB) respectively with the above mentioned solid record-developing material and with the color precursor. Such back coatings (CB) normally comprise pressure rupturable microcapsules containing a fluid color precursor in fluid form which is capable of reacting to thereby form a colored compound with the developing material in the front coating of the next adjacent sheet so that, upon impact by a machine key or application of pressure by a stylus on the top sheet, the contents of the ruptured capsules in the back coatings spill out and react with the developing material to form a colored mark on the latter which corresponds to the mark impressed by the stylus or machine key.
U.S. Pat. Nos. 2,712,507 and 3,016,308 illustrate the most common variety of carbonless impact transfer paper of the type with which the present invention is primarily concerned wherein microcapsules containing a liquid fill comprising a chemically reactive color-forming precursor are coated on the back surface of the sheet, and a dry coating of a solid co-reactant chemical for the precursor is coated on the front surface of a receiving sheet.
The pressure sensitivity of the present chemical transfer papers of the aforementioned type presents a problem in finding a balance condition on CB and CFB papers for processing over press and finishing equipment. Too much pressure, tension, etc., can cause capsular damage which effects a "blushing" on the CF side of the paper, which in turn can cause loss of image. There are also strict handling procedures which must be followed in order to prevent capsular damage in storage, and preparatory handling of roll stocks of the paper must be carefully carried out before the actual manufacturing process. During the printing operation of the papers of the carbonless impact transfer variety with which the present invention is concerned, premature and unintended rupture of the capsules affect the quality of the manifold sets, and U.S. Ser. Nos. 493,966 (now U.S. Pat. No. 4,000,087) and 505,415 (now abandoned), respectively filed July 29, 1974 and Sept. 12, 1974, commonly owned herewith, address themselves to these problems. In addition, in the development of chemically coated front and back carbonless impact transfer sheets problems of "ghosting" arise, which is an imaging of machine printed characters of CB or CFB sheets onto CF or CFB sheets when the two or more are in contact with one another, such as in files or binders.
Another area of concern in this carbonless transfer paper art is the intensity of the image produced as it relates to pressure sensitivity and further to the weight of the transfer papers. Generally, the carbonless transfer system utilizes a lightweight 12 pound base sheet with a specific CB coating weight to produce acceptable imaging on high numbered part forms, especially on high speed printers. To increase the image intensity, perhaps an additional amount of CB coating could be used and/or a lighter colored base sheet. However, the use of more CB coating may increase the pressure sensitivity problem and add to the cost of the product. And, the lighter colored base sheet could present problems in handling for manufacturing and forms handling.